In accordance with recent technological developments, personal computers (e.g, laptop and notebook computers) that are more compact and lighter than desktop computers are being manufactured and sold.
FIG. 4 is a diagram illustrating the appearance of a notebook computer (hereinafter referred to simply as a "PC" or a "system") 100. This is the same as a computer system disclosed in Japanese Design Application No. Hei 06-30003 (Our Docket No.: JA9-94-621) that was also assigned to the present applicant.
In FIG. 4, the PC 100 is a so-called "structure with a lid" that comprises a thin main body 110 and a lid 120 pivotally hinged on the main body 110.
The lid 120 has a shallow upper case 121. A pair of cylindrical protrusions 122 are integrally formed at the lower edge of the upper case 121, and are rotatively supported by the main body 110, so as to hinge the lid 120 with the main body 110. A liquid crystal display (LCD) 123, the display means for the PC 100, is provided about in the center of the opened face of the upper case 121 (i.e., the reverse side of the lid 120). The lid 120 can be opened and closed relative to the main body 110 by sliding forward and backward operating portions 124 that are formed at the front on either side of the upper case 121.
The main body 110 has a shallow lower case 111. A support board 112 having a predetermined size is provided on the lower case 111 to shield the rear portion of an upper opening in the case 111. A keyboard/TrackPoint 113 ("TrackPoint" is a trademark of IBM Corp.) is provided about in the center of the upper opening to serve as a coordinate pointing means for the PC 100. A pair of loudspeakers 114 for audio output are provided at the right and left corners at the front of the keyboard unit 113. A pair of tongue-shaped protrusions 115 that are integrally formed at the rear edge of the keyboard unit 113 so as to be pivotally hinged at the front edge of the support board 112. An indicator 115A is provided on about the rear end of the lower case 111. The indicator 115A indicates the remaining capacities of a battery, the state of a PC card, the state of a floppy disk drive (FDD) and of a hard disk drive (HDD), and the status of the system 100 when the power is on.
In FIG. 5 is shown the internal structure of the main body 110 when the lid 120 and the keyboard 113 of the PC 100 are opened. A partition wall 116, which defines a front chamber and a rear chamber, is formed in the lower case 111 by bending a thin metal plate into a predetermined shape. In the rear chamber, which is hidden by the support board 112 and the partition wall 116, are stored a system board (not shown), on the surface of which are mounted essential electric components, such as a CPU (Central Processing Unit), a system memory, a memory controller, a ROM, a video controller and an audio controller. This rear chamber is relatively narrow and the installation density for the electric components mounted in this chamber is very high. In the front chamber, forward of the partition wall 116, input/output devices, such as an HDD pack 117 and a CD-ROM drive 118, and a battery pack 119, are removably and exchangeably mounted. Several connectors are provided on the front side of the partition wall 116 for mechanically and electrically coupling the terminals of the HDD pack 117, the CD-ROM drive 118 and the battery pack 119.
There has been a remarkable improvement in the performances of the latest personal computers. This improvement stems in great part from increases in the processing speeds of the CPUs that constitute the hearts of the PCs. However, as a trade off for high speed processing, the amount of heat generated in computers has also increased. The amount of the currents that pass through the transistors in chips have grown in proportion to the increases in the operating frequencies, and accordingly, a greater amount of power is being consumed. There have been developed and manufactured many CPUs of the type which employ CMOS technology so that they consume considerably less power than do conventional bipolar semiconductors such as TTL. However, since MOS transistors also include inherent capacitive elements in their gates, the amount of heat generated has also inevitably become greater in proportion to the operating frequencies. In particular, CPUs, such as the Pentium, produced by Intel Corp., that have operating frequencies of around 100 MHz generate a lot of heat. And although the Power PC 603 ("Power PC" is a trademark of IBM Corp.), which is jointly developed and produced by Apple Computer, Inc., IBM Corp. and Motorola Corp., generates considerably less heat than does the Pentium, it still generates no small amount of heat. Thus, some electronic components may run wild, out of control, or may suffer damage due to the heat they generate by themselves. Heat generation is an especially critical problem for the above described notebook computers, because the installation density for internal electronic parts is quite high so that there is no room available for the escape of heat. Although forced cooling by employing a fan is possible with a desktop PC, in a notebook PC the space that is required for the installation of a fan can not be spared.
For electronic components that generate heat, such as CPUs, video controller chips, system memories, and co-processors in current notebook PCs, a mechanical structure is often employed wherein a cooling channel is provided by mounting components so that they contact a heat pipe for heat transmission, or wherein heat is transmitted to the exterior of a device by bringing components into contact with a heat sink (a metal case also sometimes serves as a heat sink) that is made of a heat conductive material (e.g., copper or aluminum) having a large surface area. Compared with forcible cooling using a cooling fan, since the height of a fan need not be accommodated, a natural cooling arrangement using a heat sink or a heat pipe has a smaller volume, and thus has almost no affect on the design and manufacture of compact PCs. It should be noted that a relatively complicated laminated structure is used for joining together a circuit board, electronic components, and a heat pipe.
In FIG. 6 is shown a conventional cooling structure employed for a notebook computer. A heat generating component, such as a CPU chip, is so mounted on a system board that it faces a wall of a case (e.g., the lower case 111). The case is made of a superior heat conductive material, such as a magnesium alloy. An elastic material (e.g., silicon rubber) having a relatively high heat conductive capability is adhered to the top surface of the CPU chip, and thermally communicates with a wall of the lower case 111. The lower case 111, which is integrally formed by casting, for example, has a relatively large surface area, and also serves as a heat sink. As the CPU chip generates the most heat at its top surface, with the above described structure, the heat can be effectively dispersed through the silicon rubber and the lower case 111.
On the other hand, the requirement for upgrading the performances of personal computers have been responded by various forms. Many of recent PCs permit system upgrades involving the replacement of standardly provided CPUs with other, pin compatible CPUs (generally, new CPU versions having higher processing speeds, e.g., PowerPC 603.sup.+ relative to PowerPC 603). It would be obvious to one having ordinary skill in the art that the periphery of a exchangeable CPU should be so designed with a relatively simple mechanical structure that the removal and replacement of the CPU could be easily performed. However, as is described above, the periphery of a CPU that generates much heat is so built that a close and complicated relationship exists with cooling components, such as a heat pipe and a heat sink, and it is not easy to design a mechanical device that easily permits the attachment and removal of the CPU. Conventionally, the upgrading of CPU chips is performed only for desktop PCs having extra space inside their cases that permits the inclusion of structures designed for the exchange of CPU chips.
It is highly improbable that a CPU chip exchange could be effected with the prior art shown in FIG. 6. And since heat is channeled off only from the top face of the CPU chip, a superior cooling effect would not be provided. Further, as the temperature at the portion of the lower case 111 immediately below the CPU chip would tend to be higher, this could constitute a safety hazard for a user.